Optical pulses are flashes of light that are typically generated with lasers and delivered in the form of laser beams. Short optical pulses, whose duration ranges from picoseconds (ps) to nanoseconds (ns), are employed for optical communication and sensing applications such as LIDAR (Light Detection And Ranging) and spectroscopy. Benefits of shorter optical pulses include improved target resolution in LIDAR and increased data transfer rates in optical communication.
Optical pulses can be generated using a pulse carver. The pulse carver modulates an incoming laser beam to generate a train of short optical pulses. Conventional pulse carvers include a single optical modulator and sinusoidal electrical drive limited to generating high duty cycle (i.e., >30%) pulse trains. Here, the generated optical pulse duration is fixed and inversely proportional to the repetition rate. For example, while pulses less than 10 ps can be generated at a pulse repetition rate of ˜40 GHz, ˜100 ps pulses can be generated at a repetition rate of ˜4 GHz.
Longer measurement ranges can be attained with lower repetition rates (˜MHz) in LIDAR sources. However, these LIDAR sources rely on complex, high-speed analog electronics drive optical modulators to generate and amplify short-duration electrical pulses.
Analog electronic signal processing circuits processing return-to-zero (RZ) electrical pulses require much higher bandwidth and complexity than electronics processing digital or non-return-to-zero (NRZ) signals. However, achieving distortion-free amplification of electrical RZ pulses with more than ˜30 GHz bandwidth and/or pulse durations less than ˜10 ps is difficult. Analog electronic pulse generation also is susceptible to temporal jitter.
What is therefore desired in the art is a method and architecture for producing optical pulses less than about 10 ps employing flexible pulse repetition rates. What is also desired in the art is architecture for producing short optical pulses employing digital electronics to reduce complexity and power consumption.